1. Field of the Invention
The present invention relates to a hard film, a method of forming the same, and a target for hard film formation. More particularly, the present invention relates to a wear-resistant hard film for improving the wear resistance of cutting tools, such as carbide tips, drills and milling cutters, machine parts, and dies for processing metals by plastic working, a method of forming the hard film, and a target used as a source material.
2. Description of the Related Art
Conventional cutting tools of cemented carbides, cermets or high-speed steels have been coated with a hard film of TiN, TiCN or TiAlN to improve the wear resistance of the cutting tools. Hard films of titanium nitride, titanium carbide and titanium carbide-nitride generally used for coating cutting tools for high-speed cutting and for cutting hard workpieces, such as workpieces of hardened steels have been replaced by films of Ti—Al composite nitride (hereinafter referred to as “TiAlN”) excellent in wear resistance. Addition of a third element to a two-element material, such as TiAlN, has been made in recent years in an attempt to improve the properties of the two-element material. Films of TiAlVN or (TiAlV) (CN) disclosed in, for example, JP-A 3-120354, JP-A 10-18024, U.S. Pat. No. 5,981,049 and U.S. Pat. No. 6,296,928 exhibit excellent cutting performance in cutting workpieces of materials having low hardness, such as S50C (JIS). The cutting performance of those prior art films in cutting workpieces of hard materials, such as quenched SKD (JIS) is not necessarily satisfactory. It is desired to develop films excellent in wear resistance and having higher hardness to cope with progressively increasing demand for high-speed cutting operations at higher cutting speeds. A hard film proposed in JP-A 2002-337006 is formed of a material containing at least one of Al and metals of Groups IV, V and VI, and Si, and at least one of nonmetallic elements, i.e., N, B, C and O. The description of the prior art hard film mentions only a Si content of 50% or below in connection with the optimum composition of the material. Actually, hard film having a cutting ability exceeding that of the conventional TiAlN film cannot be formed of a material prepared by simply combining the foregoing elements.
The present invention has been made in view of the foregoing circumstances and it is therefore an object of the present invention to provide a hard film having excellent wear resistance and having a high hardness higher than that of the conventional TiAlN film or (TiAlV) (CN) film, a method of forming the hard film, and a target for forming the hard film.